An extrusion apparatus for the production of multilayer synthetic resin webs can have at least two extrusion screw presses, an accumulator or combining block at which two or more streams meet, a transforming unit, and a wide or broad slit output die, from which laminated plastic strand or web emerges, the combining block has a combining channel, to which the extrusion screw presses are connected and which is connected by way of the transforming or transition apparatus to the broad-slit output die.
The definition of the combining block makes it clear that in this unit several thermoplastic layers flow together and in the combining channel are bonded as it were so as to form a multilayered or laminate but unitary flow.
The structure of the extrusion apparatus is such that the many layers of the thermoplastic foil will not mix on the way to the output die.
Further in the transition unit the transformation of the multilayered thermoplastic flow into the wide but thin thermoplastic stream occurs which emerges from the die and hardens to form the foil, sheet or plate defined as the web.
In the extrusion apparatus according to German Pat. No. DE-AS 15 04 190, the combining channel is positioned between two input channels and is connected to a tapered output die or broadslit nozzle, which extends over the length of the combining channel and, as it were, forms an inlet for the transition unit, to which the previously mentioned output die is connected.
Two flow channels are perpendicular to each other.
This is useful for fabrication, but is not free from disadvantages, since the layer thickness of the plastic layers can not be controlled without further devices.
Particularly an adjusting element is missing for the thermoplastic flow or each thermoplastic partial flow. Such an adjusting element is however important, if a plastic web is to be manufactured in which thickness of a given layer must be set and controlled and/or the layers over the entire breadth of the plastic strip must have a uniform thickness to a given small tolerance.